Abnormal responses to sensory stimulation are a commonly reported clinical feature of autism spectrum disorder (ASD). Sensory symptoms are included in the ASD profile on a number of standardized assessments, and studies based on these self- or observational reports find increased rates of sensation seeking or sensation avoidance in all sensory modalities, although the nature and affected sensory modality of these abnormalities varies greatly between individuals. Despite the general consensus that sensory abnormalities are an important clinical symptom in autism, there is little or no understanding of the underlying mechanisms. Further, because the vast majority of evidence regarding these symptoms is based solely on behavioral descriptions, it is not clear if these symptoms are truly sensory in nature or if they reflect abnormalities of general arousal levels, attention or perception. Based upon our own work and existing evidence, we suggest a model in which basic sensory function is intact in ASD and abnormalities in sensory behavior result instead from the influence of poorly modulated arousal and attention on sensory responsiveness. We propose to address this important issue using electroencephalography (EEG) and physiological measures of arousal (skin conductance and heart rate) in young adults and children with ASD. We will assess auditory and visual sensory functions including levels of sensory response, habituation and neural response recovery, and will examine the influence of arousal and attention on sensory responsiveness. A wide variety of therapeutic interventions target sensory function, but there is scant evidence for the efficacy of these treatments. Understanding the nature of sensory abnormalities and the processing level at which sensory behavior is perturbed will guide the development of more effective therapeutic interventions and/or specific pharmacological treatments. Because abnormal sensory behavior is among the most troublesome of ASD symptoms, providing a scientific basis for treatment of these symptoms would have a significant impact on the field.